Heretofore, a wire harness to be wired from an engine room in a motor vehicle to a passenger room mounts a grommet, and the grommet is attached to a through-hole provided in a vehicle body panel for partitioning a vehicle body of the motor vehicle into the engine room and the passenger room so as to protect the wire harness passing the through-hole and to waterproof, dustproof, and sound-insulate from an engine room side to a passenger room side.
The present applicant has proposed a so-called one-motion type grommet in which a vehicle body latch recess provided on an outer peripheral surface is engaged with an peripheral edge around the through-hole merely by pushing the grommet into the through-hole in the vehicle body panel from a one side.
As shown in FIG. 9A, a one-motion type grommet 100 disclosed in JP 2002-171647 A (Patent Document 1) is mounted on a wire harness W/H, the grommet 100 is attached to a through-hole 3 in a vehicle body panel 2 that partitions a vehicle body into an engine room X and a passenger room Y merely by pushing the wire harness into the through-hole 3 at the engine room X, and the wire harness W/H is drawn out from the engine room X to the passenger room Y. That is, a side of the engine room X across the panel 2 defines a pushing-in side P1 for the wire harness W/H while a side of the passenger room Y across the panel 2 defines a drawing-out side P2 for the wire harness W/H.
The grommet 100 includes a smaller diameter tubular section 103 through which the wire harness W/H passes in a close contact manner, and an enlarging diameter tubular section 104 provided on a pushing-in side end of the section 103. A smaller diameter end 104a of the enlarging diameter section 104 is contiguous with the pushing-in side end of the smaller diameter tubular section 103. A vehicle body latch recess 101 is provided in an outer peripheral surface of an enlarging diameter end 104b of the section 104.
When the grommet 100 is inserted into and attached to the through-hole 3 in the vehicle body panel 2, the smaller diameter tubular section 103 is inserted into the through-hole 3, the wire harness W/H is pushed into the drawing-out side P2 from the pushing-in side P1. Then, the enlarging diameter tubular section 104 is deflected inward and a peripheral edge around the through-hole 3 falls down in the vehicle body latch recess 101. Consequently, the grommet 100 is engaged with the vehicle body panel 2.
At this time, the enlarging diameter tubular section 104 is provided on its outer slant peripheral surface with stepped projecting ribs 105 in a peripheral direction, thereby reducing a contact area between the grommet 100 and the inner peripheral surface of the through-hole 3 to lower an inserting resistance. As shown in FIG. 9B, projecting amounts of the projecting ribs 105 are decreased in a direction to a distal end of a side surface 101a of a vehicle body latch recess 101 so that the projecting amounts of the projecting ribs become zero at the distal end of the side surface 101a. 
As described above, if the projecting amounts of the projecting ribs are gradually decreased toward the vehicle body latch recess 101, it is possible to lower an inserting force.
However, when the grommet is inserted into the through-hole, it is difficult to accord a central axis of the grommet with an axis of the through-hole 3 so that the grommet is inserted into the through-hole straightly. Consequently, the grommet is inserted into the through-hole in a slightly slant position. In this case, the vehicle body latch recess is inclined with respect to the through-hole, and there is a problem that edges of side surfaces of the projecting ribs are likely to be caught by a peripheral edge around the through-hole. In particular, in the case of a burred hole in which a burr protrudes from the peripheral edge around the through-hole, a distal end of the burr is likely to catch the side surfaces of the projecting ribs. Consequently, there are problems that the through-hole hardly falls down into the vehicle body latch recess smoothly and the projecting ribs are likely to be broken.
Patent Document 1: JP 2002-171647 A